Effects of topical tretinoin on non-sun-exposed protected skin of the elderly.

BACKGROUND: Topical tretinoin can alter some cutaneous structural alterations induced by excessive exposure to sunlight. Most human studies have focused on photodamaged or photoaged skin. Little, if any, information is available on the effects of tretinoin on chronologically or "intrinsically" aged human skin.
OBJECTIVE: Our purpose was to characterize the clinical and structural changes in non-sun-exposed skin after long-term topical treatment with tretinoin.
METHODS: Six white women, 68 to 79 years of age, applied 0.025% tretinoin cream to the inner aspect of one thigh and vehicle cream to the opposite side, once daily for 9 months. Biopsy specimens were processed for histochemistry by light microscopy and for ultrastructural analysis by transmission electron microscopy.
RESULTS: Tretinoin treatment produced a marked increase in the viable epidermal thickness and resulted in a more undulating dermoepidermal junction with prominent rete ridges. Return to a more uniform size and electron density of the basal and spinous keratinocytes was also noted. Dermal changes included increases in glycosaminoglycan deposition, elastic fibers, and new blood vessel formation.
CONCLUSION: Tretinoin substantially altered the involutional structural changes in intrinsically aged protected skin. The magnitude of the changes may be even greater than those described for photodamaged skin.